Rotate the plane about x,y,z axis in Blender
In general these:


R,X
R,Y
R,Z


Will start rotating whatever it is around the global x,y,z axises, and these:


R,X,X
R,Y,Y
R,Z,Z


Will start rotating around whatever transform type is listed in the box in the 3d View Header:



(Normal is equivalent to Local for objects, but averages selected normals when editing meshes.)

As an aside, if your objects are rotating around unexpected places check the left two buttons in this picture.